Diseases associated with the Poxviridae (smallpox, vaccinia and cowpox viruses), and Herpesviridae (HSV-1, HSV-2, HSV-8, VZV, EBV) dsDNA viruses represent major worldwide public health problems. N&N Scientific, Inc. (N&N) is developing a first of its class broad-spectrum orally bioavailable antiviral drug, N- methanocarbathymidine (N-MCT), which has exhibited potent activity against herpes and pox viruses and drug-resistant variants in vivo at doses that are non-cytotoxic in mice, rats, guinea pigs and dogs, even at doses 1000-fold higher than the therapeutic dose. These unique pharmacological characteristics suggest that N-MCT will be an ideal candidate for commercial development upon completing pre-IND studies and clinical trials. This Phase II SBIR proposal will help significantly to advance the development of N-MCT towards clinical testing. Herpes Simplex Virus (HSV) infection is a chronic disease that affects over 1 billion people worldwide, with distinct disease symptoms for each variant. Infections are commonly manifested as oral HSV-1 and HSV-2 infections, genital HSV-2 infection and HSV-8 infection in Kaposi's sarcoma, which are prevalent in sexually transmitted diseases and immunosuppressed patients. There are 500,000 new HSV-2 cases annually in the USA, and account for 75% of neonatal infections. HSV-1 infects between 20-40% of the adult population age 12 and over, and is manifested by recurrent facial cold sores that are treated predominantly with OTC remedies with limited efficacy. In children <14 years of age, as many as 35% have serologic evidence of HSV- 1 infection. To address the public health issues associated with HSV and a major commercial market, N&N proposes to develop N-MCT for the treatment and prophylaxis of genital HSV-2 infection, including neonatal infections, for which the current worldwide market is in excess of $2 billion. Current pre-IND studies of N-MCT conducted during the Phase I SBIR grant have demonstrated that N-MCT has several unique characteristics that make it particularly valuable for commercial development. These include: 1) Cytotoxicity only in HSV-infected cells 2) HSV-tk dependant antiviral activity 3) Activity against acyclovir (ACV)-resistant HSV 4) Activity against HSV-1, HSV-2, HSV-8, vaccinia and cowpox viruses 5) Greater potency than ACV across all doses 6) Activity against genital, neonatal and encephalitic HSV-2 infection, and activity against neonatal infection, even when administered 3 days post-infection, in contrast to the lack of activity of ACV 7) No cytotoxicity in mice, rats, guinea pigs and dogs at doses 1000-fold greater than the therapeutic dose 8) High oral bioavailability (80-90%) in mice, rats and dogs 9) Crosses the blood-brain barrier to eliminate HSV-2 encephalitis in mice, in contrast to a lack of efficacy f ACV 10) No toxicity in dogs administered N-MCT orally on a daily 14-day repeat dose schedule with a 14- day recovery period. 11) High drug stability at room temperature over one year with no decomposition SPECIFIC AIMS N&N proposes to develop the first of its class antiviral drug, N-MCT, for the treatment of HSV-2, including ACV- resistant variants. In the Phase I SBIR grant, N&N completed dose-range finding, 7-day acute toxicity testing in rats and dogs, PK studies in rats and dogs, as well as a 14-day repeat-dose toxicity and toxicokinetic study in dogs, including a cardiovascular assessment. N&N also completed efficacy studies in mice and guinea pigs to evaluate N-MCT against genital HSV-2 and neonatal and encephalitic infections, respectively. In this Phase II application, N&N proposes to complete an additional efficacy study in a genital HSV-2 guinea pig model resembling the human disease. In addition, we plan to complete the remaining preclinical toxicity studies, drug formulation and stability studies, plasma protein binding and metabolism and the synthesis of additional quantities of non- GMP and GMP N-MCT to advance N-MCT to clinical testing as a drug for the treatment of genital, neonatal and encephalitic HSV-2 infections. Specific Aim #1: To obtain additional preclinical efficacy data for N-MCT in a genital HSV-2 guinea pig model. Specific Aim #2: To synthesize sufficient non-GMP and GMP N-MCT for completion of preclinical studies, and formulation and stability studies, respectively. Specific Aim #3: To complete preclinical toxicology and toxicokinetic studies of N-MCT sufficient for filing an IND with the FDA. Formulation studies will define the optimal formulation for a confirmatory PK study in dogs. These studies will allow filing an IND application for the eventual initiation of Phase I clinical trials to determine the maximum tolerated dose, side effects, bioavailability, pharmacokinetics and the starting doses for Phase IIA clinical trials in patients with genital HSV-2 infections.